Recently, a personal computer (hereafter, abbreviated as a “PC”) has become widespread both in companies and home. In the PC, a CPU that is a processing circuit is incorporated and an OS (operating system) that is basic software and various application programs are installed, and various application programs are executed by the CPU under the OS. Here, the CPU is selected from plural operating frequencies from a viewpoint of suppressing such as power consumption and heat generation, and configured to operate at the selected operating frequency. The selection of the operating frequency is made by the OS in such a manner that the OS monitors a current processing situation and according to the processing situation, when processing is busy, selects a high-operating frequency whereas when processing is not busy, selects a low-operating frequency.
Although selecting a low-operating frequency takes more time to perform a same processing, when considering a total power consumption including energy conversion efficiency of a power-supply unit and power consumption in a cooling unit or the like, by lowering the operating frequency, usage efficiency of energy increases and a lower power consumption is realized.
Incidentally, some PCs have a high depth lower power consumption (deep sleep) function.
This is a function to decrease power consumption still further by stopping processing in the CPU itself (clock of the CPU is stopped), and reducing a voltage of power supplied to the CPU to the extent where content of a register in the CPU is maintained.
Here, since the OS automatically changes an operating frequency of the CPU according to a processing demand and a setting of the OS, there is a case where a high-operating frequency is selected to perform processing such as a file index function incorporated in the OS and execution of virus scan software in which taking longer time does not matter at all, eventually causing unnecessary increase in the power consumption.
Also, in such a case where the OS does not utilize the function to automatically change an operating frequency of the CPU according to a processing demand executed by the OS and a setting of the OS and instead, the OS changes a frequency of the CPU uniformly based on a particular operation or a memory access frequency per a unit time, because it is not control by a processing demand, the operating frequency becomes insufficient when staring the processing and the CPU may not be able to supply or obtain necessary data by a timing at which the data is required when staring the processing, possibly generating under-run or overrun.
In addition to reduction of power consumption, reduction of harsh noise is also a major problem. Especially when the CPU stops due to effect of the deep sleep function and when the CPU restarts operation, a large harsh noise may be generated and it is necessary to suppress the harsh noise.
The above problems are common not only in a PC but also in an information processing apparatus in general that includes a CPU to execute a program.
The following literature is known as prior art regarding operating frequency control techniques.
[Patent Literature 1] Japanese Laid-open Patent Publication No. H08-006681.
[Patent Literature 2] Japanese Laid-open Patent Publication No. 2000-148315.
[Patent Literature 3] Japanese Patent No. 3,385,811